A cleaning tool that uses a fluidic oscillator to create pressure fluctuations in the well bore adjacent a perforated interval to clean the perforations has been proposed. See SPE Paper No. 13803 entitled "Pressure Fluctuating Tool" by Payne, Williams, Petty and Bailey. Patents which are related to this technique are Galle U.S. Pat. No. 3,520,362, Galle U.S. Pat. No. 3,730,269, Baker et al U.S. Pat. No. 3,842,907, Galle U.S. Pat. No. 3,850,135 and Galle U.S. Pat. No. 4,630,689. The pulses that are created by the fluidic oscillator are fed to respective fluid-filled chambers that are communicated by an inertia tube. Oscillating or fluctuating pressures are thus generated in the annular space between the tool and the casing wall which disturb the walls of the perforations. Acoustic filters in the form of gas-filled rubber bladders are positioned in the tool above and below the primary oscillation zone to limit the propagation of the acoustic signals up and down the well bore, and to concentrate the pressure fluctuations to an adjacent interval of the perforations. The pressure fluctuations are said to remove debris from the perforations and pulverize any impermeable skin on the wall of the perforation tunnels, which can be caused by current methods of shaped charge perforating. Oil production from the perforations is thereby increased, and the ability to stimulate the formation using various techniques is also enhanced.
U.S. application Ser. No. 716,262 filed Jun. 17, 1991, now U.S. Pat. No. 5,135,051, and entitled "Perforation Cleaning Tool" in which we also are named as joint inventors, represents an improvement of the devices shown in the above-mentioned patents by providing new and improved tubular filters with transverse slots that inhibit fluid movement to better confine the pressure fluctuations to that region of the well bore between the filters. These filters provide particularly improved operation respecting those prior devices that have the elastomer bladder filters, in that they enable a shorter and smaller size tool to be used. This tool is easier to handle and does not require a large vehicle to transport it to and from a job site. The tool also has an outer diameter such that it can be operated in well casings having a fairly small size so as to work in a range of sizes that are found in most oil producing areas.
The tools shown in the above-mentioned publication and prior patents have yet another shortcoming in that the pressure fluctuations are not particularly concentrated in a manner to provide optimum cleaning of the perforations adjacent thereto. The prior devices typically employ spaced upper and lower exit ports which communicate with the outside of a small diameter sub that defines the inner wall of an exterior acoustic tank which is generally coextensive with the length of the sub. The volume of this exterior tank is so large that the intensity of the pressure fluctuations is attenuated, which reduces the cleaning power.
The general object of the present invention is to provide new and improved perforation cleaning tools where pressure fluctuations are concentrated in a much smaller volume to provide a more intense cleaning action.
Still another object of the present invention is to provide new and improved tools of the type described that produce more concentrated pressure fluctuations, in combination with an acoustic filter system that can be adjusted to fine-tune or calibrate the tool for maximum efficiency.
Yet another object of the present invention is to provide a new and improved tool of the type described which can be run and located adjacent the perforations to be cleaned without removing the production tubing from the well.